[PATCH 4/9] KVM: arm/arm64: vgic: Get rid of unnecessary process_maintenance operationjjjj
Marc Zyngier
marc.zyngier at arm.com
Tue Mar 21 06:26:52 PDT 2017
On 21/03/17 12:26, Christoffer Dall wrote:
> On Tue, Mar 21, 2017 at 11:36:19AM +0000, Marc Zyngier wrote:
>> On 20/03/17 10:58, Christoffer Dall wrote:
>>> From: Christoffer Dall <christoffer.dall at linaro.org>
>>>
>>> Since we always read back the LRs that we wrote to the guest and the
>>> MISR and EISR registers simply provide a summary of the configuration of
>>> the bits in the LRs, there is really no need to read back those status
>>> registers and process them. We can might as well just signal the
>>> notifyfd when folding the LR state and save some cycles in the process.
>>>
>>> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
>>> ---
>>> virt/kvm/arm/vgic/vgic-v2.c | 55 ++++++++++-----------------------------------
>>> virt/kvm/arm/vgic/vgic-v3.c | 47 +++++++++++---------------------------
>>> virt/kvm/arm/vgic/vgic.c | 8 +++----
>>> virt/kvm/arm/vgic/vgic.h | 4 ++--
>>> 4 files changed, 31 insertions(+), 83 deletions(-)
>>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
>>> index dfe6e5e..0172754 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v2.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v2.c
>>> @@ -22,20 +22,6 @@
>>>
>>> #include "vgic.h"
>>>
>>> -/*
>>> - * Call this function to convert a u64 value to an unsigned long * bitmask
>>> - * in a way that works on both 32-bit and 64-bit LE and BE platforms.
>>> - *
>>> - * Warning: Calling this function may modify *val.
>>> - */
>>> -static unsigned long *u64_to_bitmask(u64 *val)
>>> -{
>>> -#if defined(CONFIG_CPU_BIG_ENDIAN) && BITS_PER_LONG == 32
>>> - *val = (*val >> 32) | (*val << 32);
>>> -#endif
>>> - return (unsigned long *)val;
>>> -}
>>> -
>>
>> Getting rid of u64_to_bitmask makes me feel slightly better...
>>
>>> static inline void vgic_v2_write_lr(int lr, u32 val)
>>> {
>>> void __iomem *base = kvm_vgic_global_state.vctrl_base;
>>> @@ -51,38 +37,10 @@ void vgic_v2_init_lrs(void)
>>> vgic_v2_write_lr(i, 0);
>>> }
>>>
>>> -void vgic_v2_process_maintenance(struct kvm_vcpu *vcpu)
>>> +void vgic_v2_clear_uie(struct kvm_vcpu *vcpu)
>>> {
>>> struct vgic_v2_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v2;
>>> -
>>> - if (cpuif->vgic_misr & GICH_MISR_EOI) {
>>> - u64 eisr = cpuif->vgic_eisr;
>>> - unsigned long *eisr_bmap = u64_to_bitmask(&eisr);
>>> - int lr;
>>> -
>>> - for_each_set_bit(lr, eisr_bmap, kvm_vgic_global_state.nr_lr) {
>>> - u32 intid = cpuif->vgic_lr[lr] & GICH_LR_VIRTUALID;
>>> -
>>> - WARN_ON(cpuif->vgic_lr[lr] & GICH_LR_STATE);
>>> -
>>> - /* Only SPIs require notification */
>>> - if (vgic_valid_spi(vcpu->kvm, intid))
>>> - kvm_notify_acked_irq(vcpu->kvm, 0,
>>> - intid - VGIC_NR_PRIVATE_IRQS);
>>> - }
>>> - }
>>> -
>>> - /* check and disable underflow maintenance IRQ */
>>> cpuif->vgic_hcr &= ~GICH_HCR_UIE;
>>> -
>>> - /*
>>> - * In the next iterations of the vcpu loop, if we sync the
>>> - * vgic state after flushing it, but before entering the guest
>>> - * (this happens for pending signals and vmid rollovers), then
>>> - * make sure we don't pick up any old maintenance interrupts
>>> - * here.
>>> - */
>>> - cpuif->vgic_eisr = 0;
>>> }
>>>
>>> void vgic_v2_set_underflow(struct kvm_vcpu *vcpu)
>>> @@ -92,6 +50,12 @@ void vgic_v2_set_underflow(struct kvm_vcpu *vcpu)
>>> cpuif->vgic_hcr |= GICH_HCR_UIE;
>>> }
>>>
>>> +static bool lr_signals_eoi_mi(u32 lr_val)
>>> +{
>>> + return !(lr_val & GICH_LR_STATE) && (lr_val & GICH_LR_EOI) &&
>>> + !(lr_val & GICH_LR_HW);
>>> +}
>>> +
>>> /*
>>> * transfer the content of the LRs back into the corresponding ap_list:
>>> * - active bit is transferred as is
>>> @@ -109,6 +73,11 @@ void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
>>> u32 intid = val & GICH_LR_VIRTUALID;
>>> struct vgic_irq *irq;
>>>
>>> + /* Notify fds when the guest EOI'ed a level-triggered SPI */
>>> + if (lr_signals_eoi_mi(val) && vgic_valid_spi(vcpu->kvm, intid))
>>> + kvm_notify_acked_irq(vcpu->kvm, 0,
>>> + intid - VGIC_NR_PRIVATE_IRQS);
>>> +
>>> irq = vgic_get_irq(vcpu->kvm, vcpu, intid);
>>>
>>> spin_lock(&irq->irq_lock);
>>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>>> index 3d7796c..7880c5c 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>>> @@ -21,42 +21,9 @@
>>>
>>> #include "vgic.h"
>>>
>>> -void vgic_v3_process_maintenance(struct kvm_vcpu *vcpu)
>>> +void vgic_v3_clear_uie(struct kvm_vcpu *vcpu)
>>> {
>>> struct vgic_v3_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v3;
>>> - u32 model = vcpu->kvm->arch.vgic.vgic_model;
>>> -
>>> - if (cpuif->vgic_misr & ICH_MISR_EOI) {
>>> - unsigned long eisr_bmap = cpuif->vgic_eisr;
>>> - int lr;
>>> -
>>> - for_each_set_bit(lr, &eisr_bmap, kvm_vgic_global_state.nr_lr) {
>>> - u32 intid;
>>> - u64 val = cpuif->vgic_lr[lr];
>>> -
>>> - if (model == KVM_DEV_TYPE_ARM_VGIC_V3)
>>> - intid = val & ICH_LR_VIRTUAL_ID_MASK;
>>> - else
>>> - intid = val & GICH_LR_VIRTUALID;
>>> -
>>> - WARN_ON(cpuif->vgic_lr[lr] & ICH_LR_STATE);
>>> -
>>> - /* Only SPIs require notification */
>>> - if (vgic_valid_spi(vcpu->kvm, intid))
>>> - kvm_notify_acked_irq(vcpu->kvm, 0,
>>> - intid - VGIC_NR_PRIVATE_IRQS);
>>> - }
>>> -
>>> - /*
>>> - * In the next iterations of the vcpu loop, if we sync
>>> - * the vgic state after flushing it, but before
>>> - * entering the guest (this happens for pending
>>> - * signals and vmid rollovers), then make sure we
>>> - * don't pick up any old maintenance interrupts here.
>>> - */
>>> - cpuif->vgic_eisr = 0;
>>> - }
>>> -
>>> cpuif->vgic_hcr &= ~ICH_HCR_UIE;
>>> }
>>>
>>> @@ -67,6 +34,12 @@ void vgic_v3_set_underflow(struct kvm_vcpu *vcpu)
>>> cpuif->vgic_hcr |= ICH_HCR_UIE;
>>> }
>>>
>>> +static bool lr_signals_eoi_mi(u64 lr_val)
>>> +{
>>> + return !(lr_val & ICH_LR_STATE) && (lr_val & ICH_LR_EOI) &&
>>> + !(lr_val & ICH_LR_HW);
>>> +}
>>> +
>>> void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
>>> {
>>> struct vgic_v3_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v3;
>>> @@ -82,6 +55,12 @@ void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
>>> intid = val & ICH_LR_VIRTUAL_ID_MASK;
>>> else
>>> intid = val & GICH_LR_VIRTUALID;
>>> +
>>> + /* Notify fds when the guest EOI'ed a level-triggered IRQ */
>>> + if (lr_signals_eoi_mi(val) && vgic_valid_spi(vcpu->kvm, intid))
>>> + kvm_notify_acked_irq(vcpu->kvm, 0,
>>> + intid - VGIC_NR_PRIVATE_IRQS);
>>> +
>>> irq = vgic_get_irq(vcpu->kvm, vcpu, intid);
>>> if (!irq) /* An LPI could have been unmapped. */
>>> continue;
>>> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
>>> index 1436c2e..f5b3c25 100644
>>> --- a/virt/kvm/arm/vgic/vgic.c
>>> +++ b/virt/kvm/arm/vgic/vgic.c
>>> @@ -527,12 +527,12 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
>>> spin_unlock(&vgic_cpu->ap_list_lock);
>>> }
>>>
>>> -static inline void vgic_process_maintenance_interrupt(struct kvm_vcpu *vcpu)
>>> +static inline void vgic_clear_uie(struct kvm_vcpu *vcpu)
>>> {
>>> if (kvm_vgic_global_state.type == VGIC_V2)
>>> - vgic_v2_process_maintenance(vcpu);
>>> + vgic_v2_clear_uie(vcpu);
>>> else
>>> - vgic_v3_process_maintenance(vcpu);
>>> + vgic_v3_clear_uie(vcpu);
>>> }
>>>
>>> static inline void vgic_fold_lr_state(struct kvm_vcpu *vcpu)
>>> @@ -642,7 +642,7 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>>> if (unlikely(!vgic_initialized(vcpu->kvm)))
>>> return;
>>>
>>> - vgic_process_maintenance_interrupt(vcpu);
>>> + vgic_clear_uie(vcpu);
>>> vgic_fold_lr_state(vcpu);
>>
>> nit: If you moved vgic_*_clear_uie() into vgic_*_fold_lr_state, you
>> could get rid of this call, extra prototypes, and save yourself the
>> extra check. Not a big deal though.
>>
>
> I thought about this, but the problem is that strictly speaking, you
> don't need to consume any LRs to set the underflow, you just need enough
> in the AP list, and it's theoretically possible that you have nr_lrs+1
> interrupts in the AP list which have all been migrated away.
But isn't that a problem we already have, independently of reworking the
above?
> So, it would require something like this including a rework in
> flush_lr_state to work with the following patch which only calls
> vgic_fold_lr_state when there are in fact anything live in LRs:
>
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index e5cf930..4b1feef 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -601,10 +601,8 @@ static void vgic_flush_lr_state(struct kvm_vcpu *vcpu)
>
> DEBUG_SPINLOCK_BUG_ON(!spin_is_locked(&vgic_cpu->ap_list_lock));
>
> - if (compute_ap_list_depth(vcpu) > kvm_vgic_global_state.nr_lr) {
> - vgic_set_underflow(vcpu);
> + if (compute_ap_list_depth(vcpu) > kvm_vgic_global_state.nr_lr)
> vgic_sort_ap_list(vcpu);
> - }
>
> list_for_each_entry(irq, &vgic_cpu->ap_list_head, ap_list) {
> spin_lock(&irq->irq_lock);
> @@ -623,8 +621,12 @@ static void vgic_flush_lr_state(struct kvm_vcpu *vcpu)
> next:
> spin_unlock(&irq->irq_lock);
>
> - if (count == kvm_vgic_global_state.nr_lr)
> + if (count == kvm_vgic_global_state.nr_lr) {
> + if (!list_is_last(&irq->ap_list,
> + &vgic_cpu->ap_list_head))
> + vgic_set_underflow(vcpu);
> break;
> + }
> }
>
> vcpu->arch.vgic_cpu.used_lrs = count;
>
> What do you think?
I think this deserves a patch of its own. Also, how about renaming
clear_uie to clear_underflow?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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